Nitinol can return to its undeformed shape when heated at a particular temperature (shape memory effect) and it can also undergo large deformation without permanent deformation (superelasticity). So why does Nitinol have this shape memory effect? The key is to understand how the atoms rearrange themselves in response to deformation.
Shape memory effect:
It is necessary to understand the properties of Nitinol that make it a popular choice for self-expanding stents. This lesson discusses Nitinol's characteristics from a material point of view.
While the metallurgical properties are beyond the scope of this lesson, we can study their effects on the mechanical behavior of Nitinol using Ansys simulation. This workshop demonstrates Ansys software’s capability to model superelasticity.
Lesson Video — Compare Superelasticity versus Plasticity on a Spring Model Workshop
The geometry file can be found here.
- Please utilize the mm, kg, N unit system when solving the Ansys simulation models.
- Please also note that the results you obtain in these nonlinear analyses may differ slightly from those shown in the videos. Numerical round-off due to finite machine precision can be affected by the choice of the operating system, the number of cores, and the type of parallel processing (shared-memory vs. distributed-memory). Moreover, nonlinear contact and solution algorithms are often improved in each version of our software, so some changes are expected when comparing results between different releases. Thus, your results may differ slightly (within typical engineering tolerances) from the presented results, but this is to be expected for nonlinear analyses, especially for numerically unstable (e.g., underconstrained) models that may be utilized in this course.
Completed simulation files from the above example can be found here.